Dear Diary

Information Description
Category Forensics
Difficulty Medium

Image Not Showing Possible Reasons
  • The image file may be corrupted
  • The server hosting the image is unavailable
  • The image path is incorrect
  • The image format is not supported
Learn More →
autopsy

題目敘述

If you can find the flag on this disk image, we can close the case for good! Download the disk image here.

Hint: If you're observing binary data raw in the terminal you may be misled about the contents of a block.

解題過程

  1. 這題給了一個 image 檔 disk.flag.img.gz. 先透過 gunzip disk.flag.img.gz 指令將它解壓縮
  2. 這題會用到一個工具叫做 autopsy 來分析硬碟來分析硬碟檔。直接在 terminal 打上 autopsy,它會給一個 URL,把這個 URL 打開就會試等等工具的使用介面(以這題來說就是 http://localhost:9999/autopsy)
    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →
  3. 在正式開始分析之前有一系列步驟要先完成,可以想成要先建一個專案資料夾放等等要用到的東西、這次分析的基本資訊等等
    • 首先是創建一個 case,點選 New Case,填寫 case 名稱 (Case Name),說明 (Description) 和研究者 (Investigator names) 可不填
      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →

      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →
    • 接著要新增該 case 的主機,點擊 Add Host 並填寫 Host 名稱 (Host Name),其他欄位一樣是選填,按照預設過去就可以了
      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →

      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →
    • 再來就是匯入 image 檔,點選 Add Image > Add Image File 匯入硬碟檔,硬碟檔位置 (Location) 記得要填寫絕對位置,其他一樣維持預設值即可,
      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →

      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →

      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →

      Image Not Showing Possible Reasons
      • The image was uploaded to a note which you don't have access to
      • The note which the image was originally uploaded to has been deleted
      Learn More →
  4. 分析直接點擊 Analyze,因為要猜 flag,所以選擇 Keyword Search
    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →
  5. 策略是 flag 的長相為 pico{XXX},所以先來猜會不會有 pico 字串的檔案
    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    好吧!很可惜沒有
  6. 下一個策略是 flag 可能會是一個 txt 檔,那搜尋 .txt 試試看
    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    Image Not Showing Possible Reasons
    • The image was uploaded to a note which you don't have access to
    • The note which the image was originally uploaded to has been deleted
    Learn More →

    仔細觀察其中一段檔案會發現每一個檔案都包含 flag 的一部分,組成起來就是完整的 flag 了
  • Image Not Showing Possible Reasons
    • The image file may be corrupted
    • The server hosting the image is unavailable
    • The image path is incorrect
    • The image format is not supported
    Learn More →
    : picoCTF{1_533_n4m35_80d24b30}

註記

  1. 如果發現輸入 autopsy 無法執行並得到 "can't open log: autopsy.log at /usr/share/autopsy/lib/print.pm line 383." 的 error message,就換成 sudo autopsy 執行
  2. 這題沒特別放 image file,因為檔案太大了

參考資料